About 280 million years ago, all
the continents were assembled together into a supercontinent--Pangea.
Present day “continental" Oregon
did not exist. About 170 million years ago, Pangea broke apart
along boundaries resembling present day continental margins. The
break-up started with a spreading rift system (red dashed line)
forcing North America to move northwest and creating the Atlantic
Ocean as it widened. The splitting-up of Pangea motion initiated
the coastal subduction zone that strongly influences Oregon geology.
The blue dotted line shows the ancient shoreline of western North
America at this time. |
|
As Pangea broke-up and spread apart, the
North American continent overrode the Pacific Ocean floor
and created a SUBDUCTION ZONE along the Oregon coast (and
other places). The continental material is lighter and tends
to “float” on
the heavier basaltic oceanic material. At about 60 miles in
depth, the down-going slab melts and sends plumes of molten
rock (magma) to the surface. In places, these bodies of magma
emerge as volcanoes and other types of volcanic eruptions. |
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AND THEN …..
